A satellite, more specifically, a geostationary telecommunications satellite, is typically in the form of a rectangular parallelepiped, on which are defined a north face and a south face, an east face and a west face, a front face and a rear face. The north, south, east and west faces are thus named corresponding to the cardinal points of the planet around which the satellite is placed. The front face is the one directed towards the planet, the rear face is the opposite face.
The satellite comprises a plurality of items of equipment mounted on its different faces, such as antennas, radiators or also motor nozzles. As a result, the spatial requirement is a major challenge in the design of satellites and their equipment, the total external surface area limiting the number and dimensions of the equipment that can be installed.
More specifically, each item of equipment is subjected to its own particular constraints. For example, an antenna must not have a field of view that is obscured by the other equipment. Motors, such as plasma thrusters, generate a plasma jet which risks damaging neighbouring equipment. A solar panel must be exposed to the sun over the greatest possible surface area.
Thus, positions and minimum distances between the equipment must be respected in order to guarantee their correct operation, so that the surface area on the outside of the satellite is rapidly overloaded.
The problem will be explained more specifically using the example of radiators for geostationary satellites, i.e. satellites which are fixed relative to a point on a planet.
A satellite can comprise numerous items of equipment which generate temperature increases during their operation, and which therefore require cooling. Furthermore, the satellite in space receives solar radiation, which increases the temperature of the equipment. These temperature increases can damage the equipment, which therefore has to be cooled. To this end, provision can be made to thermally link thermally radiative surfaces, more commonly called radiators, to the equipment, which radiators have the function of removing heat to cold space.
The radiators are positioned on the external surface of the satellite so as not to be subjected to temperature increase, i.e. they are, so far as possible, shielded from the solar radiation. To this end, a radiator is generally mounted on the north face or the south face of the satellite, so that the radiative surface of the radiator, turned towards space, is positioned on the north face or the south face. In fact, the north and south faces of the satellite are the least exposed to the solar radiation, so that the radiative face of the radiator receives little or no solar radiation.
The document U.S. Pat. No. 6,102,339 (WU et al.) illustrates an example of a satellite in which the north and south faces are each covered by a radiator.
However, the size of the radiators is limited by the dimension of the north and south faces. Now, the larger the radiative surface area, the more efficient the dissipation of heat. The dimensions of the north and south faces of the satellite are limited in particular by the fact that, in order to be able to be put into orbit, the satellite is placed in a launch vehicle beforehand. The satellite must then be as compact as possible.
Thus, it is known to install deployable radiators which are folded during the launch of the satellite and deployed when the satellite is in orbit. The documents FR 2 823 182 (ALCATEL), U.S. Pat. No. 5,833,175 (CAPLIN) and WO 03/059740 (ASTRIUM) each present an example of such radiators. The deployed radiative surface area is however limited by the other equipment of the satellite, such as the antennas which, as has already been said, must not be obstructed when the radiators are deployed. Furthermore, such radiators are not completely shielded from the solar rays. In fact, while the satellite generally remains in the plane of the planet's equator, the angle of the incident solar rays can have a variable inclination depending on the position of the planet in relation to the sun. As a result, solar rays can reach the north and south faces of the satellite, and therefore the radiators, reducing their efficiency.
Mirrors reflecting the sun's rays, known as Optical Solar Reflectors (OSR), can be used to cover the radiators, in order to further reduce the temperature increase due to the sun's rays. However, such mirrors increase the manufacturing costs of the satellite. Furthermore, they degrade over time, not ensuring efficient protection throughout the operation of the satellite.
The abovementioned document U.S. Pat. No. 6,102,339 (WU et al.) proposes to install a blocking device, mounted on a rotating solar panel on the satellite in order to follow the solar rays. The blocking device is then interposed between the radiators and the solar rays, the inclination of which with respect to the north and south faces of the satellite allows them to reach the radiators.
However, such an additional blocking device increases the overall spatial requirement on the body of the satellite in an undesirable manner. The manufacturing costs are also increased. Furthermore, such a blocking device must be folded at launch, then deployed once the satellite is in orbit. The kinematics of the deployment of the blocking device, combined with that to be developed for the solar panels and optionally the radiators, makes the design of the satellite more complex.
A need therefore exists for a novel satellite, in which the overall spatial requirement is reduced so that the items of equipment do not impede one another, without however making the design more complex.